The present invention relates to a real-image finder optical system provided in a camera independently of a photographing optical system, and more specifically, to a real-image finder optical system that is capable of displaying information in the field of view thereof.
A real-image finder that is provided independently of a photographing optical system includes an objective optical system having a positive power, an erecting optical system for erecting a reversed image formed by the objective optical system, and an eyepiece optical system for observing the erected image in a magnified fashion. The above described optical systems are provided in this order from an object side. In a camera having zoom lens, the finder optical system is also provided with zoom function. Namely, at least one lens group of the objective optical system is movable along an optical axis to change the magnification of the finder according to the zooming of the photographing optical system.
In general, the real-image finder is provided with an information display element in the vicinity of an image plane of the objective optical system to display information in a field of view of the finder. The displaying element may be a transparent member on which an opaque pattern is formed to thereby shield incident light from an object. A frame indicating a photographing range, a frame indicating a focusing zone, a photographing mode of the camera, and other numeric information are displayed as a shadow of the opaque pattern in the field of view of the finder. A liquid crystal display element or the like may be used to display variable information.
In the above-described conventional real-image finder, however, since the display element is disposed in the vicinity of the image plane of the objective optical system on which the eye of a user is focused, when dust particles are adhered on the displaying element during assembling of the finder, the dust particles are conspicuous in the field of view of the finder. If the number of surfaces arranged in the vicinity of the image plane is reduced, the possibility that the dust particles are conspicuous in the field of view is reduced. For this purpose, there has been known an arrangement that the lens of the objective optical system is spaced from the vicinity of the image plane. However, since conventional finders are designed such that the patterns formed on the information display element are directly observed through the eyepiece optical system, the displaying element cannot be positioned apart from the vicinity of the image plane for the clear observation of the patterns. Thus, there still remains a problem that the dust particles are conspicuous in the field of view and prevent observation.